B.B. Kovalev

Galvanomagnetic properties and electronic structure of Pb1?x?ySnxVyTe under pressure

We study the galvanomagnetic properties in weak magnetic fields (4.2 ? T ? 300 K, B ? 0.07? T) and the Shubnikov-de Haas effect (T = 4.2 K, B ? 7 T) in single crystal Pb1?x?ySnxVyTe alloys under variation of alloy composition (x = 0.05?0.20, y ? 0.01) and hydrostatic compression up to 15 kbar. The increase of vanadium impurity content leads to the p-n-conversion and to a transition in the insulating phase due to the pinning of Fermi level by the donor-type deep vanadium impurity level situated under the bottom of the conduction band. We found that pressure induces a decrease of the activation energy of the vanadium level, the n-p-inversion of the conductivity type at low temperatures and an insulator?metal transition. In the metallic phase, a sharp increase of the Hall mobility (up to 3???105?cm2? V?1? s?1) and appearance of Shubnikov-de Haas oscillations are observed at helium temperature. The pressure and temperature coefficients of vanadium deep level energy are determined, and the diagram of the electronic structure rearrangement for Pb1?x?ySnxVyTe under pressure is proposed.

Ferromagnetism in Diluted Magnetic Semiconductors Pb1-x-yGexCryTe

Magnetic and galvanomagnetic properties of Pb1-x-yGexCryTe (x=0.02-0.20, y=0.01-0.08) solid solutions have been investigated. It was found that the magnetic susceptibility of these alloys contains two contributions: a paramagnetic Curie-Weiss share (T<50 K) due to the paramagnetism of Cr3+ ions and a high temperature ferromagnetic share (T<300 K). Dependence of the concentration of paramagnetic centers on the composition of the matrix was obtained. The magnetic field dependences of the Hall coefficient in the vicinity of the metal-insulator transition were measured and the main parameters of charge carriers in terms of the two-band conduction model were estimated. The experimental results are discussed in the framework of the electronic structure model, assuming varying electrical and magnetic activities of Cr ions as function of germanium content in the alloys.

Pressure Studies of the Conductivity Mechanisms in Electron‐Irradiated Pb1—xSnxSe

The dependence of the Hall constant on the magnetic field (B ≤ 7 T) in the vicinity of the insulator–metal transition induced by pressure (P ≤ 18 × 108 Pa) in Pb1—xSnxSe (x ≤ 0.03) alloys irradiated with electrons (T ≈ 300 K, E = 6 MeV, Φ ≤ 7.1 × 1017 cm—2) has been investigated. The main parameters of charge carriers were obtained by comparing experimental data with theoretical dependences of Hall constant on the magnetic field calculated in the frame of the two-band model and found to be in good agreement with them. It was shown that in the vicinity of the insulator–metal transition at least three conduction mechanisms should be taken into account.

Localised defect states in electron-irradiated Pb1-xSnxSe alloys

The effect of pressure on the galvanomagnetic properties of electron-irradiated n-Pb1-xSnxSe (0.07<or=x<or=0.125) has been investigated. The electron concentration as a function of pressure is used to determine the parameters of the band of radiation-induced resonant states and to reconstruct the energy spectrum of Pb1-xSnxSe alloys irradiated with electrons.

Insulator-Metal Transition in Diluted Magnetic Semiconductor Pb1-x-ySnxVyTe under Pressure

The galvanomagnetic properties in weak magnetic fields (4.2T300 K, B0.07 T) as well as Shubnikov-de Haas effect (T=4.2 K, B7 T) in the single crystal Pb1-x-ySnxVyTe (x=0.20, y0.01) under hydrostatic compression up to 15 kbar have been investigated. It is shown that under pressure the decrease of activation energy of vanadium deep level, n-p-inversion of the conductivity type at low temperatures and insulator-metal transition take place. In the metallic phase sharp increase of the Hall mobility and appearance of Shubnikov-de Haas oscillations at helium temperature are observed. The pressure coefficient of vanadium level energy is determined and the diagram of the electronic structure rearrangement for Pb1-x-ySnxVyTe under pressure is proposed.

Rearrangement of electronic structure of Pb1-x-ySnxVyTe under pressure

The galvanomagnetic properties in weak magnetic fields (4.2≤T≤300 K, B≤0.07 T) and the Shubnikov-de Haas effect (T = 4.2 K, B≤7 T) in the single crystal Pb1-x-ySnxVyTe (x = 0.05-0.20, y≤0.01) alloys at atmospheric pressure and under hydrostatic compression up to 15 kbar have been investigated. We found that the increase of the vanadium impurity content leads to the p-n-conversion, transition to the insulating phase and to the pinning of Fermi level by the deep impurity level, lying under the bottom of the conduction band. Under pressure a decrease of the activation energy of the vanadium level, the n-p-inversion of the conductivity type at low temperatures and an insulator-metal transition occur. The pressure and the temperature coefficients of vanadium deep level energy are determined and the diagram of the electronic structure rearrangement for Pb1-x-ySnxVyTe under pressure is proposed.

Insulator-metal transition in Pb1-xGexTe doped with chromium under pressure

The galvanomagnetic effects in the n-Pb1-xGexTe (x=0.02-0.13) alloys, doped with chromium, at the temperatures in the range of 4.2≤T≤300 K and under hydrostatic compression of up to 17 kbar have been investigated. The insulator-metal transition, induced by pressure in Pb1-xGexTe: Cr (x=0.10) alloy, was revealed. Using the experimental data in the frame of two-band Kane dispersion relation the pressure dependences of electron concentration and Fermi energy were calculated. The pressure coefficient of chromium deep level energy was obtained and the diagram of the electronic structure reconstruction under pressure was proposed.

Insulator–metal-type transitions induced by electron irradiation in gallium-doped PbTe-based alloys

We report the results of our study of the electron irradiation effect (E = 6 Me V, Φ ≤ 8 × 10 17 cm -2 ) on the galvanomagneticv (4.2 K ≤ T ≤ 300 K, B ≤ 0.1 T) properties of gallium-doped PbTe, n-Pb 1-x Ge x Te (0.04 ≤ x ≤ 0.06) and Pb 1-y Sn y Te (y = 0.19, 0.23) narrow-gap semiconductors. Depending on the features of the initial electronic structure of the alloys, a p-n-inversion, a transition from metal to insulating or from insulating to metal-type conductivity and an increase in the free electron density under electron irradiation were revealed. The rate of defect generation under irradiation was found to be abnormally high for A 4 B 6 materials. The activation character of the temperature dependences of the galvanomagnetic parameters, caused by the presence of deep gallium-induced defect levels in the gap, was observed for the alloys in the insulating state. The results were explained assuming that electron irradiation of gallium-doped PbTe-based alloys creates primarily donor-like defects, which leads to an increase of the electron concentration and a change in the occupancy of the allowed and localized bands. Additionally, electron irradiation seems to cause a change in the charge activity of gallium centres within the bulk, providing a high rate of defect generation.

Radiation defect band in Pb1-XSnXSe(x≤0.03) alloys irradiated with electrons

The effect of hydrostatic pressure on the galvanomagnetic properties has been investigated. It was shown that the hole concentration increase under pressure due to the motion of the energy bands at the Brillouin zOne L-point and the flow of electrons from the valence band to the radiation defect band Et1. Obtained experimental data were used to determine the parameters of irradiation-induced defect band Et1 by comparing theoretical and experimental pressure dependencies of hole concentration.

Kinetics of the accumulation of radiation defects during the high-dose electron irradiation of Pb1−xSnxSe alloys

The kinetics of the variation of the electron concentration in electron-irradiated (T≈300 K, E=6 MeV, Φ⩽7.1×1017 cm−2) n-Pb1−xSnxSe (x=0.2 and 0.25) alloys in the vicinity of the metal-insulator transition induced by electron irradiation are investigated. The principal parameters of the energy spectrum of the irradiated alloys are determined by comparing the experimental and theoretical dependences of the electron concentration on fluence. It is shown that agreement between the theoretical and experimental data is possible only under the assumption that the defect production rate decreases with increasing fluence, and a model, within which the main defect formation mechanism in the alloys investigated is the formation of complexes of primary radiation defects with structural defects typical of the as-grown crystals, is proposed.